Deep brain stimulation (DBS) and other related procedures involving implantation of electrical stimulation leads within the brain of a patient are increasingly used to treat disorders, such as Parkinson's disease, dystonia, essential tremor, seizure disorders, obesity, depression, restoration of motor control, and other debilitating diseases via electrical stimulation via stimulation of one or more target sites, including the ventrolateral thalamus, internal segment of globus pallidus, substantia nigra pars reticulate, subthalamic nucleus (STN), or external segment of globus pallidus. DBS has become a prominent treatment option for many disorders, because it is a safe, reversible alternative to lesioning. For example, DBS is the most frequently performed surgical procedure for the treatment of advanced Parkinson's Disease. There have been approximately 30,000 patients world-wide that have undergone DBS surgery. Consequently, there is a large population of patients who will benefit from advances in DBS treatment options.
During DBS procedures, at least one burr hole is meticulously cut through the patient's cranium so as not to damage the brain tissue below, a large stereotactic targeting apparatus is mounted to the patient's cranium, and a cannula is scrupulously positioned towards the target site in the brain. A stimulation lead is then introduced through the cannula, through the burr hole, and into the parenchyma of the brain, such that one or more electrodes located on the lead are strategically placed at a target site in the brain of the patient. Once the lead is properly positioned, the portion of the lead exiting the burr hole is subcutaneously routed underneath the patient's scalp to an implantable pulse generator (IPG) implanted in the patient at a site remote from the burr hole (e.g., the patient's shoulder or chest region). Further details discussing the treatment of diseases using DBS are disclosed in U.S. Pat. Nos. 6,845,267, 6,845,267, and 6,950,707, which are expressly incorporated herein by reference.
Significantly, it is crucial that proper location and maintenance of the lead position be accomplished in order to continuously achieve efficacious therapy. This is especially so with DBS applications, in which cases, the target site (or sites) that is intended for electrical stimulation may be about the size of a pea and is located deep within the patient's brain. Thus, lead displacements of less than a millimeter may have a deleterious effect on the patient's therapy. Therefore, it is important that the electrode(s) of the lead be accurately located at the target site and that such electrode(s) be securely maintained at the target site during and after implantation of the lead.
To address these issues, a cranial burr hole plug is installed within the burr hole during the implantation procedure to hold the stimulation lead in place, as well as to seal the burr hole. Typically, the burr hole plug may be composed of a number of components, including a ring-shaped base, an insert or retainer, and a cap, that are integrated together to form the burr hole plug.
In particular, before the stimulation lead is introduced through the burr hole, the ring-shaped plug base is placed about the burr hole, and is then permanently mounted to the patient's cranium using conventional means, such as screws. The stimulation lead is then introduced through the plug base and into the parenchyma of the brain. Notably, any displacement of the portion of the lead exiting the burr hole may result in the unwanted translation of the electrodes positioned in the brain relative to the target site, thereby requiring the lead to be repositioned—a time-consuming process.
Thus, once the lead is properly located at the tissue site, the retainer is installed within the plug base (typically in an interference arrangement, such as a snap-fit arrangement) to temporarily secure the lead, thereby preventing migration of the lead relative to the target site during subsequent manipulation of the proximal end of the lead and installation of the cap. In one example, the retainer has a disk having a slot for receiving the lead and a clamping mechanism that can be rotated within the slot towards a mating surface on the disk to frictionally clamp the received lead therebetween. The clamping mechanism may have one or more locking mechanisms that can engage or disengage complementary locking mechanisms on the disk to prevent rotation of the clamping mechanism. The portion of the stimulation lead exiting the retainer can then be bent downward towards the plane of the disk into a recess formed in the plug base, and the cap can be installed onto the plug base over the retainer to permanently secure the lead within the recess. Further details regarding these types of burr hole plugs are disclosed in U.S. Patent Publication No. 2002/0156372.
It can thus be appreciated from the foregoing that the burr hole plug serves as an anchor for the implanted DBS lead as well as a cover for the entry point into the brain. Therefore, it is important for this component to be robust, well-fitting, and easy to use. Importantly, the burr hole plug should be designed such that lead does not migrate or dislodge once the lead is implanted into the brain and anchored by the burrhole plug. While prior art burr hole plugs have proven to be useful in the DBS context, there are still improvements that can be made.
As one example, the clamping mechanism used to clamp the stimulation lead should provide even pressure on the lead once the clamping mechanism is moved into position to lock the lead into place.
As another example, it is common in prior art devices for the plug base of the burr hole plug to be screwed into the burr hole in the cranium. Another design issue is that the curvature of craniums between infants and adults is different, yet the burr hole plug must be a “one-size-fits all” design. To accommodate for such differences in curvature, it is common for the burr hole plug base to be flexible, so that the burr hole plug base will bend during and after placement into the burrhole in order to conform to the shape of the cranium. However, such bending and flexing of the plug base can cause the components making up the burr hole plug to deform and stick relative to each other, thereby affecting the operation of the clamping action on the lead and, in addition, resulting in an unstable attachment of the burr hole plug to the cranium.
In yet another example, the plug base of the burr hole plug is secured to the cranium with fasteners, e.g., usually screws. There may be flanges or wings extending from the plug base and these flanges or wings are present because they contain holes that the fasteners/screws are placed into for securing the plug base to the cranium. The use of wings or flanges extending from the plug base, however, can cause fitting challenges because, depending on the curvature of a particular cranium, the flanges or wings may not sit flush over the surface of the cranium, i.e., may be “lifted” on one part.
There, thus, remains a need for improved burr hole plug designs to address issues such as conforming the burr hole plug to different cranium shapes and. preventing skewing of the clamping mechanism used to retain the medical device in the burr hole plug.